The present invention relates to hydraulic pumps.
It is well known to utilize hydraulic pumps to provide a source of pressurized fluid in a large number of environments. Several different types of pumps are available and chosen to meet the particular requirements of the intended application.
A particularly demanding application is in an automotive transmission where a pump is used to supply pressurized fluid to the transmission over a wide range of operating conditions. Typically the pump is driven by the transmission and its rotational speed will therefore vary with the engine speed. At the same time the flow requirements may fluctuate significantly over the normal operating cycle demanding high flow rates at low engine speed and vice-versa.
Because the pumps operate over the wide speed range normally encountered in an engine, the flow rate of the pump is typically much greater than is required for operation of the transmission and its power consumption is increased. Typical operating pressures are in the order of 250 psi and therefore the power consumed by the pump is significant but manageable. On the other hand, newer transmission arrangements are increasing the pressure with which the systems will operate and therefore the energy loss becomes significant.
Various attempts have been made to control the energy loss by utilizing different hydraulic valving but these introduce complexity and cost into the transmission system.
The higher pressures currently being contemplated also introduce additional mechanical loading into the pump system which in turn must be compensated for in the overall design. As a result the cost, complexity and weight of the transmission may be increased. Besides the variability in the operating conditions, the automotive transmission application is particularly arduous due to cost sensitivity of automotive components. The components must not only be very reliable but must also be provided at minimum costs. As a result, it is common practice to integrate the components with other transmission components wherever possible to maintain the cost and weight of the components at a minimum.
It is therefore an object of the present invention to provide a hydraulic pump and a hydraulic circuit incorporating such as pump in which the above disadvantages are obviated or mitigated.
In general terms, the present invention provides a hydraulic pump having a housing and a pumping element rotatable in the housing. A pair of pumping chambers are defined between the housing and the pumping element with each chamber having an inlet to receive fluid from a source. A pair of outlets are provided for each of the inlets and the outlets of one pair are arranged diametrically opposed to the corresponding outlets of the other pair. In this manner the hydraulic forces acting upon the pumping element are balanced.
By providing a pair of outlets, for each inlet the flow from one of the outlets may be diverted to the inlet above a certain flow rate leaving the other outlet to provide the required flow rate at operating pressure. By diverting one of each pair of outlets to their respective inlets, the balance on the pumping element is maintained.
In a further aspect of the invention there is provided a hydraulic system including a pump having an housing and a pumping element rotatable within the housing. A pair of chambers are defined within the housing each having an inlet to transfer fluid from a hydraulic source to the chamber. A pair of outlets are associated with each of the inlets with the outlets of one pair being diametrically opposed to the corresponding outlets of the other pair. A valve is connected to a corresponding outlet of each pair and is operable to direct fluid from the one outlet to its respective inlet.